The subject matter of this application is related to the subject matter of copending U.S. application Ser. No. 299,500.
This invention relates to a method and apparatus for file deletion in a bubble cassette memory and, more particularly, to a method and apparatus for deleting a file in a bubble cassette memory for storing a machining or part program.
In numerical control devices having an internal memory for storing a part program, it is conventional practice to use a paper tape as a storage medium for writing the part program into the memory and for preserving the information which is stored in the memory. A tape reader and tape puncher are connected to the numerical control device, the former for transferring data from the tape to the internal memory, and the latter for reversing the process. A system of this type which relies upon a paper tape storage medium is not entirely satisfactory since the paper tape has a comparatively short life, is difficult to handle and does not always provide the desired reliability since reading errors are often encountered. Moreover, system costs are raised due to the tape reader and puncher.
In recent years cassette memories of the type that rely upon magnetic bubbles have been developed as storage media to replace the older paper tape configurations. Numerical control systems employing such bubble cassette memories have been disclosed and put into practical use. In such numerical control systems, single units or files of machining data such as machining programs delivered consecutively by a numerical control device are stored in a number of bubble cassette memories. In processing a machining program the desired machining program is read out of the bubble cassette memory holding the program and is stored in a memory located within the numerical control device. Numerical control processing is then performed by the numerical control device in accordance with that particular machining program.
When a number of machining programs have been stored in a bubble cassette memory in the manner described above, there are occasions where an operator may wish to delete one of the machining programs from the memory. For example, a situation may arise in which an NC machining operation on the basis of the machining program is no longer required. When such is the case it is preferred that the unnecessary machining program be deleted from the bubble cassette memory to create a blank portion into which a new machining program may be written, for then more effective use can be made of the bubble cassette memory. When an unnecesary or old machining program is merely deleted from memory, however, the new machining program, if it is longer than the old program, cannot be stored in the blank portion formerly occupied by the old program. On the other hand, when the new program is shorter than the old, storage in said blank area from which the old program has been deleted is possible but results in some blank space being left over. It is therefore not possible to exploit the bubble cassette memory effectively.
Methods do exist for deleting a record from a magnetic disc or magnetic tape. For example, refer to "Introduction to File Compilation" by Masaki Yamatani, published July 25, 1980, pp. 35 to 43. Specifically, a method of deleting a record from a magnetic disc device includes steps of (1) reading the master record to be deleted, (2) tagging a specific data field of the master record to indicate deletion, and (3) writing the master record back into its original location. With this method, however, a blank space is not created following deletion of the record, thereby preventing effective utilization of the memory. A method of deleting a record from a magnetic tape device includes steps of (1) providing two magnetic tapes, one constituting the old master file which stores the record that is to be deleted, and the other constituting a new master file, (2) providing a deletion record having a key field identical with that of the master record to be deleted, (3) reading master records from the old master file sequentially to discriminate whether the respective key fields coincide with the key field of the deletion record, (4) writing a master record, which has been read from the old master file, directly into the new master file when the key field of that record does not coincide with the key field of the deletion record, and then reading the next master record, (5) refraining from writing a record into the new master file when its key field does coincide with the key field of the deletion record, and (6) repeating the foregoing steps to store only the required records in the new master file without a blank space, formed by deleting a record, being left between adjacent records in the new master file. With this method, however, two master files, the new and the old, are required, and considerable processing time is expended. The result is an increase in apparatus size and higher operating costs.
The foregoing conventional methods of deleting data in magnetic tapes and discs can be applied directly to bubble cassette memories but are unsatisfactory in terms of effective memory utilization, processing time and cost, as described above.